by Patrick L. Cahalan

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Histogram

Going along with last week’s post about exposure, this time I’m going to dial in a bit on a particularly helpful tool for getting exposure right on a DSLR (apologies to you film nuts out there!).

Short version, the histogram is something you can see on your camera’s LCD display (see your owner manual if you don’t know how to find it). It is designed to show you which parts of the image are well exposed, or if the image is very under- or over-exposed. It usually looks like this:

Normal Histogram

Ideally, you want this to be bell-curve shaped, as above. This denotes an image that is neither under or overexposed.

Conversely, here are examples of “bad” histograms (I use quotes because sometimes you will want your histograms to look like this, but that’s the exception).

UnderexposedOverexposed

In other words, you ideally want your histogram to be clustered around the center, and higher up vertically.

Now, suppose you snap a shot, and notice it looks like the overexposed version above. That basically means too much light got through to your sensor, and you can compensate by decreasing the exposure. So take off one stop (via aperture, shutter speed, or ISO as you like) and take another photo. Repeat as necessary.

Same thing goes, in the opposite direction , for underexposed images. Open your camera up an extra stop and take a shot, and see if it improves (and repeat as needed).

Depending on your make/model of camera, you may also be able to view histograms not just as a single graph, but one each for red, green, and blue. That’s even better! It gives you greater ability to re-shoot in the field as needed, with less chance of having to spend a ton of time in Photoshop fixing things afterward. There are few things I enjoy less than fixing things in PS after the fact; I’d much rather spend the time shooting.

Next time I’ll continue on the theme of exposure, with a brief overview of the Zone System.

And here’s something well exposed, just for fun. Can’t have all the pics in a post be about dry technical stuff, now can we??

Mt. Hood, OR

PS snow is a right pain-in-the-you-know-where to expose. I’ll also be using that as an example next week.